Nickel and titanium alloys are well known in the art. For example, U.S. Pat. No. 3,351,463 to Rozner et al issued Nov. 7, 1967 discloses nickel-titanium alloys. These alloys undergo temperature dependent transition from one solid phase to another solid phase. At a relatively colder temperature, the solid phase is the martensitic phase. Upon heating, the alloy passes through an intermediate rhombohedral phase. Finally, a high temperature body-centered cubic crystal is reached, referred to as austenite.
These nickel-titanium alloys exhibit shape memory, due to martensitic phase transformation. At a relatively colder temperature, below the transition temperature, the alloy can be placed in a deformed condition. Upon heating to a temperature greater than the transition temperature, the alloy returns to its original or neutral condition. The temperature range at which the alloy flexes between the deformed and the neutral conditions is known as the transition temperature range.
Known binary nickel and titanium alloys do not have a transition temperature range exceeding 250 degrees F. It is desirable to have a transition temperature range exceeding 300 degrees F to substantially increase the usefulness of the alloys. These alloys can then be used in systems having temperatures exceeding 300 degrees F.
By adding palladium to the nickel-titanium alloy, the transition temperature range can be increased to greater than 300 degrees F. Achievement of this high temperature transition range by adding palladium to a nickel-titanium alloy is disclosed in Kachin et al "High Temperature Shape Memory Effects in TiNi-TiPd System Alloys" translated from Dokl, Akad. Nauk. SSSR, Vol 257(1), 1981. The addition of palladium to the nickel-titanium alloy, however, reduces the fabricability, or ductility, of the alloy.